Temporally determinate disk access (extended abstract): an experimental approach

The current level of unpredictability associated with the traditional approach for disk service is unacceptable to realtime applications. Consequently, early real-time applications avoided the use of disk drives and operated entirely in main memory. In order to significantly reduce this variability, we should have a better understanding of its cause(s), and use this knowledge in the design of better device drivers. A typical disk I/O operation incorporates delay components such as: seek delay, rotational delay, off-surface transfer delay, and host transfer delay. The last two delay components typically show very small variability. On the other hand, seek and rotational delays have shown variability in the order of IO’s of milliseconds. 2 Design Considerations and the Run-Time System